As it becomes possible to fit more and more circuit elements onto a single substrate, a correspondingly larger number of interconnects may need to be fabricated on the substrate to connect the circuit elements to off-substrate circuitry. Conventional interconnects are typically formed on the same side of the substrate as the circuit elements (the xe2x80x9cfrontsidexe2x80x9d of the substrate), and terminate at contact pads formed around the perimeter of the frontside of the substrate. With each increase in the number of circuit elements on a single substrate, the contact pads and interconnects typically become more crowded around the perimeter of the substrate. This may lead to reducing the size of the interconnects to squeeze them into the available space. The reduced interconnect size may lead to various problems, such as a high interconnect resistance caused by the small cross-sectional area of the interconnects.
In various specific implementations, the placement of interconnects on the substrate frontside may cause other problems as well. For example, the interconnects that connect the firing mechanisms in an inkjet printhead die to external circuitry are typically formed on the same side of the substrate as the ink nozzles. Thus, these interconnects may be exposed to printing inks during printhead use, which may degrade or damage the interconnects. Furthermore, continued exposure to the inks may lead to the eventual failure of the printhead.
The present invention provides a method of forming a through-substrate interconnect for a circuit element in a microelectronics device. The device is formed on a substrate having a frontside and a backside, and includes a circuit element formed on the frontside of the substrate connected to a contact pad formed on the backside of the substrate by the through-substrate interconnect. The method includes forming a first interconnect structure extending into the substrate from the frontside of the substrate, at least partially forming the circuit element such that the circuit element is in electrical communication with the first interconnect structure, and forming a second interconnect structure extending into the substrate from the backside of the substrate after forming the first interconnect structure such that the second interconnect structure is in electrical communication with the first interconnect structure.